The present invention relates to a bolt or pin clamp for use with an external fixator.
Currently, there are many bone deformities or fractures that external fixators can correct. Such devices such as those designed by Illzarov for example. Usually such an external fixator comprises rings or plates also designated as fixation plates connected by threaded rods or struts to manipulate angulations, translation and length discrepancies of bones. Furthermore the fixation plates are connected to bony structure by means of pins which usually extend through the rings. The pins are connected to the plates by means of bolts and nuts. Usually pins having different diameters will be used depending on the special situation near the fracture. For that reason several bolts with openings having respective diameters have to be used.
U.S. Pat. Nos. 5,630,814 and 5,681,309 provide one solution to adapt a bolt in order to be used to clamp different pin or wire sizes. For that reason the bolt comprises an opening which is provided with cross section that is tear drop-shaped. Thereby the pin is in connection with the bolt and the fixation plate via three contact zones all of which are provided with respective surfaces.
The shape of the drop shaped opening as well as the fact that the pin is clamped via plane surfaces has several drawbacks. Due to the shape it may be possible that it comes to gaping such that the sidewalls of the opening will be moved with respect to each other. Furthermore it is possible that the area above the opening fractures in case extraordinary tightening forces are necessary.